Warm-up, heavy rain raise specter of flooding, landslides

Originally published March 3, 2014 at 10:12 pm
Updated March 4, 2014 at 5:22 pm

Snoqualmie Falls was in full swing Monday, with melting snow in the mountains causing rivers in the region to swell. The little falls at left add volume to the flow of the Snoqualmie River. More heavy rain is forecast for Wednesday.

Trucks on the eastbound lanes of Interstate 90 near Fall City wait for Snoqualmie Pass to reopen Monday.

The heavy snow that shut Snoqualmie Pass on Monday will soon transition to heavy rain, bringing the possibility of floods and landslides later this week, according to the National Weather Service.

Because of dangerous driving conditions, the Washington State Department of Transportation closed Snoqualmie Pass over Interstate 90 for more than 16 hours, from 12:15 a.m. to 4:30 p.m. Monday, spokesman Meagan McFadden.

The pass had received 22 inches of snow in 24 hours, which led to avalanches and landslides and caused trees to fall onto the highway. The pass had to be closed for debris cleanup and avalanche control.

However, traffic congestion was at a minimum at the closure points at North Bend and Ellensburg because drivers took alternate routes at Highway 2 over Stevens Pass or Highway 12 over White Pass, McFadden said. On Monday, traction tires were advised on all three passes and oversize vehicles were prohibited.

Stevens Pass was expected to be closed from milepost 56 to milepost 72 between 2 and 6 a.m. Tuesday for avalanche control.

By Wednesday, with warmer temperatures forecast, the snow is expected to shift to heavy rain, according to the National Weather Service. Half an inch to 2 inches of rain is expected for the lowlands, while the Central Cascades and Olympics may get 2 to 5 inches. Flooding is a concern, especially near the Skokomish, Snoqualmie and Chehalis rivers.

At the Snoqualmie River near Snoqualmie Falls, the gauge height — the height of a river above a reference point — rose to 6 feet, an increase of 2½ feet since Saturday, according to the U.S. Geological Survey.

“All that water is going to run off right into the rivers,” meteorologist Johnny Burg said.

Because there is uncertainty over where the heaviest rain will fall, residents in flood-prone river valleys are urged to monitor the latest weather and river forecasts, the weather service says in its hydrologic outlook. Warmer temperatures and high snow levels will increase runoff with creeks and streams.

Landslides are also possible, with steep coastal bluffs and hillsides most susceptible, Burg said. Rainfall has increased soil moisture to high levels in the lowlands, and the expected rainfall will put extra pressure on soil stability.

The rain-snow mix also increases the avalanche danger, so crews will monitor slopes near Snoqualmie Pass on Tuesday morning and bring down loose snow if needed, McFadden said.

“We are hoping not to close it again, but weather conditions change so rapidly,” McFadden said. “I wouldn’t be surprised if we had to close it again.”